250-500cc heat causing my '11 wr300 to cut out and stall. what could it be

Here's my long winded story. What's your diagnosis please?

2 rides ago: About two hours into my ride the head pipe smacked a rock riding through some densely wooded single track, which put a 1" dia. x 0.5" deep cone shaped dent in it about 12" downstream of the cylinder. Shortly thereafter my bike started cutting out and stalling making the infamous "boowah" sound. I was able to limp it back to my truck, but it was cutting out and stalling intermittently in most speeds/gears and throttle openings. A plug swap didn't help and it was clean like it wasn't sparking much or very hot. The bike ran perfectly prior to this during short local rides and during 4 -5 hr long enduros w/out issue, so I'm sure jetting was not the cause. Did smacking the rock w/the pipe cause this, or was it just coincidental timing that something else reared its ugly head? Back home I discovered the inside of the carb/reed block manifold was severely cracked and had a small hole in the top where the clamp screw is located. Swapped it for a new one. Also checked the reeds, air cleaner and serviced the carb to ensure float level was good and jets and air/fuel circuits were clean (Keihin PWK AS, 42 PJ, AS 1.5, red JD needle 3rd clip, 175 main, 50:1). Installed 2 new gaskets on the reed cage. Verified power valve operation, tank venting, no fuel blockage, and repacked the oem silencer (use heat and chisel off the rivets). Verified coolant was circulating and that coolant was not entering the cylinder. I run the oem dash, but have the headlight disconnected. Recently installed a Rekluse Z-Start Pro. Bike started w/out issue at home and ran great while putting around the front yard and street for 20 minutes or so. No real load applied to engine during this short trial. Problem solved? Bike has about 170 hrs and is about 50 hrs into it's second top end. Also have the high comp head on it. Compression seems fine, but I haven't tested it to verify.

1 ride ago: The bike ran fine after letting it warm up sufficiently in the parking lot and for the first few miles (same place and weather conditions as before). After 20 to 30 minutes and several decent technical climbs that loaded the engine it started behaving the same way again: boowah, then dead. This time it was worse. Couldn't keep it going for 1/4 mile w/out it cutting out (like their is a spark or fuel delivery or jetting issue) and eventually stalling. Finally was unable to start it after a few miles of this. Took a break to pull off the carb to double check the plug. Carb was fine, plug was swapped for a new one and was too clean and looking like it was not working. Bike fired up after 15-20 minutes of trail side work, but took many kicks. Within a few minutes of riding, same thing would happen. Limped it back to the truck again barely for diagnosis. Fiddled w/the AS for awhile. Bike got really hot doing this and started knocking, so turned in the AS to keep it rich. When I could keep it idling it would die as soon as I put it in gear w/the clutch pulled in. Took it home for more diagnosis. Thinking it's electrical now...

Checked plug cap/wire resistance at 7k ohms. Wire was 2k ohms, so cap must be 5k ohm like it says on the boot. Checked voltage of lead into the voltage regulator (brown wire from stator) at 12v with engine running. While turning the flywheel using a power drill with the plug out the plug is sparking blue sparks when ground to the engine block, I'm getting about 16 volts at the brown wire and about 8 volts at the red wire that enters the coil/cdi (the drill is only able to turn the flywheel less than idle speed hence the low voltage readings I suspect). Not sure how to test for 35-36 volts w/the voltage regulator disconnected like the workshop manual states. All grounds to frame were clean and tight. Didn't find any chafed wires either. Haven't pulled the flywheel off yet to check the stator; waiting for a flywheel puller to arrive. Will be difficult to mimic same conditions that cause the issue at home. Hmmm.

So what's causing my bike to cut out and stall after it's warmed up?

Did you ever look at the exhaust outlet of the engine? You smacked the pipe... maybe its unseated? A friend rode his KTM all day with the pipe dislodged from the motor but none of the gang could figure out what was wrong with his bike. Took days to figure out what was going on.

Dirtdame, Like I said I installed 2 new gaskets on the reed block; one between the boot/manifold and the reeds, the other between the reeds and the cylinder, and the boot/manifold is brand new. So I'm sure an air leak there is ruled out. I pulled the tank off and opened the petcock and fuel drains w/out issue, so no obstruction and tank is vented to the atmosphere w/the oem tube. So you're saying if the plug is not sparking it would be dark rather than light? How so? The plug was slightly wet like it had some gas on it, but otherwise looked clean like it hadn't sparked much at all (this was the original plug before I swapped it for a new one). The new plug looked the same when I limped it back to my truck.

Long stroke, yes I removed the pipe when I got it home and replaced the two o-rings and reinstalled it. Then I repacked the silence and completely and cleaned carbon from the core and spark arrestor. I checked the inside of the pipe for any loose carbon or other obstruction and found nothing. I did notice about 1/16" buildup of carbon on the inside, but from what I'm told and have experienced that does not really adversely affect engine performance.

Kelly, I double checked the carb vents. I've had vapor lock before so I know what to look for and what it sounds like. Pipe and silencer are good to go as well as I explained to Long_Stroke. I'm thinking it's either something w/the stator or the Ducati cdi/coil. I spoke w/Bill of BMP yesterday (also ordered the correct flywheel puller from him). In short, he indicated that in his experience most heat related failures of any motorcycles (dirt or street) are due to trigger failures. So after I get the flywheel and stator off I'll have a better idea and can share photos on this thread of my findings. I've also read of resistors failing in the sparkplug caps. I measured the resistance in mine as I described in my original post and it was fine, but that was at ambient temperature. I did put a hair dryer on it for several minutes to try to mimic a heated condition and the resistance fluctuated less than 10 ohm, which is insignificant. I suppose I'll simply replace the cap and wire just to cheaply eliminate that possibility and see how my bike responds putting around the yard for an extended time to see how the engine responds.

So do you think it's a faulty trigger, timing issue, faulty coil or cdi? Can the voltage regulators go bad and wreck havoc on the ignition system or create shorts? This is all new to me and it's baptism by fire coming up to speed w/the entire electrical system.

When the bike died in the woods and you were trying to figure it out, did you check spark?

I'd also consider a complete carb swap, either back to the original carb or another PWK if you have access to one. That is a good way to completely eliminate one variable.

Does it shut completely off? Does it start right up? Look at my post''s, i had to replace the cdi. The pipe dent has nothing to do w it. My is effed up and still runs like a champ!

To Brian, if you need a Mikuni for carb elimination purposes I'm right down the road from you somewhere on this Island.

No bikes around that you can swap parts off of for testing? It's not that much to check but its about all black box stuff

Good question. I did not during the first ride; I just replaced the plug, then started the bike and kept going...barely. I don't remember if I check for spark during my second ride trail side pit stop. That would have been smart to do. I did swap the plug, but I was thinking it was jetting related at that time and wasn't thinking it was electrical.

I have the stock TMX still. I have never used it. I could swap that in for the PWK (w/the appropriate jets of course), but I'm highly dubious that my problem is carb related since I had no carb issues leading up to the problem. It's worth a try though.

Yes, it would shut off completely. Occasionally I could kick it over again before rolling to stop if I had enough momentum. Sometimes it would restart on the first kick. Other times it would take a dozen. I'll look for your posts. Can you provide a link? I don't think it's the pipe either. I've seen guys ride with pipes much worse than mine and not have the same cutting out and stalling issues I'm experiencing.

I agree it sounds electrical. However, swapping the carb is an easy way to totally eliminate that as a cause.

Next time it dies, check the spark.

After that, I'd probably go through systematically checking/swapping ignition parts. There isn't much to check: check that you have +12v at the coil, check the coil resistance, check the stator resistance, check wire continuity. After that, start swapping parts, it's really only the coil and the stator on these, if you have 12V.

Thanks! I'm in the Eagledale area on the southeast side of the island. We should hookup and ride Tahuya or Green Mtn this summer. I have the original TMX still. What jets are you running? I may want to "borrow" your stator, cdi/coil and/or regulator. Time to knock the dust off my CR 500 while my poor WR recoups from a disorder of its central nervous system.

Yes, the bottom of the plug is clean with some slight burning of the ground electrode. I wonder if when I smacked the pipe that I somehow knocked the ignition out of timing ever so slightly? But wouldn't that manifest itself immediately after starting the bike (when it's cold) and not just when the bike it hot? My problem is only occurring after the bike is warmed up and being ridden hard. I think I'm going to put it all back together this evening and ride it around my property (I live on a hill) until that symptom reappear and check a bunch of the electrical parts. More to come...

Sounds like shrubitup may be a willing donor since we apparently live only a few miles apart. You're right, it's not much to check, but if it's in the black box then I'm seriously considering putting some cash down for an '02 cr250 ignition and jd dual map cdi like Motorhead and ajaxauto did. Think I'd rather have the coil separate from the cdi now...

Ha ha I'm at Fort Ward... JD jet kit 32.5 410 white needle third clip with his richer nozzle tho too.